Patent EA-000950-B1 (EA)
Title: Process for the recovery of precious metal values from aqueous ammoniacal thiosulfate leach solutions
Inventor: VIRNIG MICHAEL J
IPC: C22B11/08
Filed: 1997-05-28
Abstract: 1. A process for the recovery of precious metals from ores containing the precious metals comprising (a) providing an aqueous ammoniacal thiosulfate leach solution containing the precious metal values; (b) contacting the aqueous ammoniacal thiosulfate leach solution containing the precious metal values with a precious metal extraction reagent for a time sufficient to form an ammonium thiosulfate complex with the extraction reagent thereby extracting or removing the precious metal values from the aqueous ammoniacal thiosulfate leach solution;  (c) stripping the precious metal values from the extraction reagent; and (d) recovering the precious metal from the aqueous stripping solution. 2. A process as defined in claim 1, wherein the precious metal is gold or silver. 3. A process as defined in claim 1, wherein the extraction reagent in step (b) is one having guanidyl functionality. 4. A process as defined in claim 3 wherein the extraction reagent having guanidyl functionality has the formula   wherein R1 and R5 is selected from the group consisting of H, an ion exchange resin carrier and hydrocarbon groups having up to 25 carbon atoms and provided further that when one of the R groups R1 through R5 is an ion exchange resin carrier, the remaining R groups are H or an aliphatic or aromatic hydrocarbon group having up to 25 carbon atoms. 5. A process as defined in claim 4 wherein when one of the R groups R1 through R5 is an ion exchange resin carrier to which the guanidine functionality is chemically bonded to the carrier, the remaining R groups are all hydrogen providing an unsubstituted guanidyl functionality. 6. A process as defined in claim 4 wherein the extraction reagent having guanidyl functionality is a water insoluble guanidine compound soluble in a water immiscible hydrocarbon solvent and having a pKa value at 25 degree C. greater than 10. 7. A process as defined in claim 6 wherein the pKa value is greater than 12. 8. A process as defined in claim 6 wherein the guanidine compound is N,N'-bis(cyclohexyl)-N"-isotridecyl guanidine. 9. A process as defined in claim 6 wherein said hydrocarbon solvent is kerosene or a petroleum distillate fraction having a flash point of 150 degree F (65,56 degree C) or higher. 10. A process as defined in claim 6 wherein the organic phase, is contacted with a caustic solution having a pH above 11 thereby stripping the precious metal values from the organic phase and providing an aqueous strip solution now containing the precious metal values in a more concentrated form than the original leach solution. 11. A process as defined in claim 10 wherein the aqueous strip solution is separated from the organic phase from which the precious metal values have been stripped. 12. A process as defined in claim 11, wherein the precious metals are removed by electrolysis of the aqueous strip solution. 13. A process as defined in claim 10 wherein the aqueous caustic stripping solution is a NaOH or KOH solution. 14. A process as defined in claim 10, wherein the extraction reagent in step (b) is a quaternary amine mixed with a weak organic acid. 15. A process as defined in claim 14 wherein the quaternary amine has the formula  R6R7R8R9N<+>X<-> wherein X<-> is an anion, each of R6, R7 R8 and R9 is a hydrocarbon radical containing up to 25 carbon atoms, and wherein the sum of carbon atoms in the total of R6, R7, R8 and R9 is at least 16. 16. A process as defined in claim 15 wherein at least one of the R6, R7 R8 and R9 groups will have at least 6 carbon atoms and no more than two of the R6, R7 R8 and R9 groups will be methyl. 17. A process as defined in claim 15 wherein three of the R6, R7 R8 and R9 groups are alkyl groups having at least 6 carbon atoms. 18. A process as defined in claim 15, wherein the quaternary amine is tri (C8-C10) methyl ammonium chloride. 19. A process as defined in claim 14 wherein the weak organic acid is an alkyl phenol having the formula III or IV    wherein Rlo is hydrogen or an electron-withdrawing group selected from the group consisting of Cl, Br   wherein R12 is hydrogen or a hydrocarbon radical having from 1 to 25 carbon atoms with the proviso that the total number of carbon atoms in R11 and R12 is from 6 to 30; n is an integer from 0 to 4; and R11 is an alkyl group having from 1 to 25 carbon atoms, preferably from 7 to 12 carbon atoms. 20. A process as defined in claim 14, wherein the quaternary amine is tri (C8-C10) methyl ammonium chloride and the phenol is selected from the group consisting of heptylphenol, octylphenol, nonylphenol and dodecylphenol. 21. A precious metal ammonium thiosulfate complex of a precious metal selected from the group of gold and silver and an extractant for said precious metal, said extractant being an amine selected from the group consisting of a guanidine compound and a quaternary amine. 22. A precious metal complex as defined in claim 21 wherein the precious metal complex is a gold thiosulfate complex. 23. A complex as defined in claim 21, wherein said guanidine as the formula.  24. A complex as defined in claim 23, wherein the guanidine compound is N,N'-bis (cyclohexyl)-N"-isotridecyl guanidine. 25. A complex as defined in claim 23, wherein said guanidine compound is chemically bonded to an ion exchange resin. 26. A complex as defined in claim 23 wherein the guanidine compound chemically bonded to the resin is unsubstituted guanidine. 27. A complex as defined in claim 21, wherein the quaternary amine cation has the formula R6, R7 R8 and R9N<+> wherein each of R6, R7 R8 and R9 is a hydrocarbon radical containing up to 25 carbon atoms, and wherein the sum of carbon atoms in the total of R6, R7 R8 and R9 is at least 16. 28. A complex as defined in claim 27, wherein three of the R6, R7 R8 and R9 groups are alkyl groups having at least 7 carbon atoms. 29. A complex as defined in claim 28, wherein the quaternary amine is tri-(C8-C10) methyl ammonium cation. 30. A process for the recovery of precious metals from aqueous thiosulfate solutions the precious metals comprising (a) contacting the aqueous thiosulfate solution containing the precious metal values with a precious metal extraction reagent for a time sufficient to form a thiosulfate complex with the extraction reagent thereby extracting or removing the precious metal values from the aqueous thiosulfate solution; (b) stripping the precious metal values from the xtraction reagent; and  (c) recovering the precious metal from the aqueous stripping solution.